Cutting elements comprising superhard cutting tables are used extensively in cutting, milling, grinding, drilling and other abrasive operations. For example, such cutting elements are widely used within drill bits used for boring into the earth in the oil and gas drilling industry.
Superhard cutting tables typically consist of a mass of superhard particles, typically diamond or cubic boron nitride, bonded into a coherent, polycrystalline conglomerate. As an example, polycrystalline diamond (PCD) is a super-hard material comprising a mass of inter-grown diamond grains and interstices between the diamond grains. PCD is typically made by subjecting an aggregated mass of diamond grains to an ultra-high pressure and temperature. Material wholly or partly filling the interstices is referred to as filler or binder material. PCD is typically formed in the presence of a sintering aid, which promotes the inter-growth of diamond grains. The sintering aid is commonly referred to as a solvent/catalyst material for diamond, owing to its function of dissolving diamond to some extent and catalysing its re-precipitation. A solvent/catalyst for diamond is understood to be a material capable of promoting the growth of diamond and the formation of direct diamond-to-diamond bonds at a temperature and pressure at which diamond is thermodynamically stable. As examples of solvent/catalyst materials there may be mentioned cobalt, iron, nickel, and manganese, and alloys including one or more of these materials. Consequently, the interstices within the sintered PCD product are typically wholly or partially filled with residual solvent/catalyst material.
It is common for superhard cutting tables to be supported on a support or substrate of some kind. For example it is known for superhard cutting tables to be supported on a cemented carbide substrate or support. This substrate provides a convenient means for attachment of cutting element comprising the cutting table and substrate within a tool body. It may also advantageously provide support in cases where the superhard cutting table is brittle. A typical cutting element incorporating a superhard cutting table comprises a disc shaped cutting table, for example a disc shaped PCD table, on a generally cylindrical substrate, e.g. a generally cylindrical cemented carbide substrate, e.g. tungsten carbide substrate. The substrate may have the same or similar diameter to the disc-shaped cutting element. The cemented carbide substrate may itself contain a binder material, for example cobalt, nickel, iron, manganese, or an alloy of one or more of these materials.
The term cutting “table” is used extensively in the field. While the structure of such a table in the field is commonly a substantially flat disc, no particular shape is required for the cutting “table”, other than that of a shape capable of providing a surface which can apply a cutting or abrasive action.
Superhard cutting tables are often produced by placing the components necessary to form the cutting table in particulate form on a substrate in a reaction capsule, which is then placed in the reaction zone of a high pressure/high temperature apparatus, and subjected to high pressure and high temperature (HPHT). For example superhard particles, e.g. diamond particles, may be placed in combination with solvent/catalyst particles, e.g. cobalt, on a substrate, e.g. a cemented tungsten carbide substrate, in such a capsule, and subjected to HPHT. During the HPHT treatment, the catalyst/solvent material particles in the component mix, and/or also any binder materials present in the cemented carbide substrate, e.g. cobalt or the like, may migrate through and/or into the mass of superhard particles to act as a catalyst, these catalyst/solvent materials causing the ultrahard particles to bond to one another. Once manufactured the cutting element comprises a cemented carbide layer and a cutting “table” layer, the latter comprising a coherent matrix of superhard particles (e.g. diamond particles) bonded to one another with interstices containing binder material between those superhard particles. The production of cutting tables supported on a substrate in this way is described in many references, for example, in WO 2008/015622, US 2006/0060391, and U.S. Pat. No. 7,533,740.
It is also known in the art, e.g. from WO 2008/015622, that increased presence of solvent/catalyst material in the superhard element can compromise the thermal stability of the cutting element. Treatments to mitigate this are known. For example US 2006/0060391 describes treatment of a PCD body by removing substantially all of the catalyst material from a selected region of the body by a suitable process, e.g. acid leaching, aqua regia bath, electrolytic process, or combinations thereof.
WO2010/117834 and U.S. Pat. No. 7,533,740 are examples of references which describe securement of preformed thermally stable diamond cutting tables to substrates.
U.S. Pat. No. 7,487,849 describes a cutting element that includes a substrate, a thermally stable polycrystalline diamond layer and a metal interlayer between the substrate and the diamond layer, and a braze joint securing the diamond layer to the substrate. The metal interlayer may be of a suitable thickness to provide a shock absorbing ability to the cutting element.